Identification and characterization of Eimeria tenella apical membrane antigen-1 (AMA1)

Bioefficacy of dietary inclusion of Nannochloropsis oculata on Eimeria spp. challenged chicks: clinical approaches, meat quality, and molecular docking

Although anticoccidial drugs have been used to treat avian coccidiosis for nearly a century, resistance, bird harm, and food residues have caused health concerns. Thus, Nannochloropsis oculata was investigated as a possible coccidiosis treatment for broilers. A total of 150 1-day-old male Cobb broiler chicks were treated as follows: G1-Ng: fed a basal diet; G2-Ps: challenged with Eimeria spp. oocysts and fed basal diet; G3-Clo: challenged and fed basal diet with clopidol; G4-NOa: challenged and fed 0.1% N. oculata in diet, and G5-NOb: challenged and fed 0.2% N. oculata. Compared to G2-Ps, N. oculata in the diet significantly (P < 0.05) decreased dropping scores, lesion scores, and oocyst shedding. Without affecting breast meat colour metrics, N. oculata improved meat quality characters. At 28 days of age, birds received 0.2% N. oculata had significantly (P < 0.05) higher serum levels of MDA, T-SOD, HDL, and LDL cholesterol compared to G2-Ps. Serum AST, ALT, and urea levels were all decreased when N. oculata (0.2%) was used as opposed to G2-Ps. Histopathological alterations and the number of developmental and degenerative stages of Eimeria spp. in the intestinal epithelium were dramatically reduced by 0.2% N. oculata compared to G2-Ps. Molecular docking revealed a higher binding affinity of N. oculata for E. tenella aldolase, EtAMA1, and EtMIC3, which hindered glucose metabolism, host cell adhesion, and invasion of Eimeria. Finally, N. oculata (0.2%) can be used in broiler diets to mitigate the deleterious effects of coccidiosis.

Immunoprotective effects of DNA vaccine against Eimeria tenella based on EtAMA3 and EtRON2L2

Eimeria tenella is the most pathogenic and harmful intestinal parasitic protozoan. Recombinant DNA vaccines open options for promising strategies for preventing avian coccidiosis, replacing chemical drugs and live oocyst vaccines. Two important antigenic proteins, EtAMA3 (also known as SporoAMA1) and EtRON2L2, act together to promote the invasion of E. tenella sporozoites. In this study, a recombinant DNA vaccine, designated pcDNA3.1(+)-AR, was constructed based on EtAMA3DII, EtRON2L2D3, and EtRON2L2D4. Chickens were intramuscularly immunized with different doses (25, 50, or 100 μg) of pcDNA3.1(+)-AR to evaluate its immunoprotective effects in vivo. The chickens in the 50 μg and 100 μg groups had higher cytokine concentrations (interleukin 2, interferon-gamma, and interleukin 10), and lesion scores (81.9% and 67.57%, respectively) and relative oocyst production (47% and 19%, respectively) reduced compared with the unchallenged group, indicating partial protection against E. tenella. These results suggest that pcDNA3.1(+)-AR is a promising vaccine candidate against avian coccidiosis.

Eimeria tenella pyrroline -5-carboxylate reductase is a secreted protein and involved in host cell invasion

Chicken coccidiosis, which caused by Eimeria spp, is a parasitic protozoal disease. At present, control measures of this disease depend mainly on anticoccidial drugs and live vaccines. But these control strategies have drawbacks such as drug resistance and limitations in live vaccines production. Therefore, novel control approaches are urgently need to study to control this disease effectively. In this study, the function and characteristics of the pyrroline-5-carboxylate reductase of Eimeria tenella (EtPYCR) protein were preliminary analyzed. The transcription and translation level were analyzed by using qPCR and Western blot. The results showed that the mRNA transcription and translation levels of EtPYCR were higher in unsporulated oocysts (UO) and second generation merozoites (Mrz) than that in sporulated oocysts (SO) and sporozoites. Enzyme activity showed that the enzyme activity of EtPYCR was also higher in the UO and Mrz than that in the SO and sporozoites. Immunofluorescence localization showed EtPYCR was mainly located on the top of sporozoites and the whole cytoplasm and surface of Mrz. The secretion assay indicated that EtPYCR was secretion protein, but not from micronemes. Invasion inhibition assay showed that rabbit anti-rEtPYCR polyclonal antibodies can effectively inhibit sporozoite invasion of DF-1 cells. These results showed that EtPYCR possess several important roles that separate and distinct from its conversion 1-pyrroline-5-carboxylate (P5C) into proline and maybe involved in the host cell invasion and development of parasites in host cells.

Efficacy of dietary supplements of Glycyrrhiza glabra (Licorice) and maduramicin alone or in combination with Eimeria tenella infected chicks: A clinical study and molecular docking

Background

Coccidiosis is one of the most economically significant poultry diseases worldwide, caused by the pathogenic Eimeria species, and is characterized by decreased weight gain (WG) and failure to grow due to malabsorption, low feed conversion rate, bloody diarrhea, and dehydration.

Aim

This study investigated the effectiveness of licorice root extract (LRE) in controlling cecal coccidiosis to determine whether its combination with maduramicin could help alleviate the pathological, biochemical, and histopathological effects of cecal coccidiosis in Sasso broiler chicks.

Methods

A total of 125 one-day-old Sasso broiler chicks were categorized into five equal groups (n = 25), each consisting of five replicates (n = 5 per replicate). G1-LE received a basal diet supplemented with LRE (3 g/kg); G2-ME received a basal diet containing maduramycin (0.5 g/kg); and G3-LME received a basal diet containing LRE and maduramicin together with the same rates. G4-E (positive control) and G5-N (negative control) received no additives in their feed. Birds in groups (G1-4) were challenged on day 14 of the experiment by orally intercropping a 1 ml suspension of Eimeria tenella sporulated oocysts.

Results

Groups of birds fed on LRE and maduramicin separately or together appeared to be in good condition where no deaths or clinical abnormalities were observed, based on the analysis of clinicopathological examination. Compared with the G4-E positive control, the dropping scoring and oocyst shedding of groups G1-LE, G2-ME, and G3-LME along the 10th-day post-challenge (dpc), as well as macroscopic and microscopic lesions scoring at the 7th dpc, was considerably lower. The dual supplementation use of LRE and maduramicin in G3-LME's reduced the harmful effects of coccidian, which appeared only as a mononuclear cellular infiltration and a small number of oocysts invading the intestinal glands. Molecular docking revealed that LRE and maduramicin interacted with E. tenella DNA polymerase, E. tenella apical membrane antigen 1, and microneme protein binding sites resulting in reduced E. tenella replication and invasion.

Conclusion

The inclusion of LRE and maduramicin, individually or in combination, in the diet might effectively mitigate the detrimental effects of coccidiosis.

The microneme adhesive repeat domain of MIC3 protein determined the site specificity of Eimeria acervulina, Eimeria maxima, and Eimeria mitis

Understanding the determinants of host and tissue tropisms among parasites of veterinary and medical importance has long posed a substantial challenge. Among the seven species of Eimeria known to parasitize the chicken intestine, a wide variation in tissue tropisms has been observed. Prior research suggested that microneme protein (MIC) composed of microneme adhesive repeat (MAR) domain responsible for initial host cell recognition and attachment likely dictated the tissue tropism of Eimeria parasites. This study aimed to explore the roles of MICs and their associated MARs in conferring site-specific development of E. acervuline, E. maxima, and E. mitis within the host. Immunofluorescence assays revealed that MIC3 of E. acervuline (EaMIC3), MIC3 of E. maxima (EmMIC3), MIC3 of E. mitis (EmiMIC3), MAR3 of EaMIC3 (EaMIC3-MAR3), MAR2 of EmMIC3 (EmMIC3-MAR2), and MAR4 of EmiMIC3 (EmiMIC3-MAR4), exhibited binding capabilities to the specific intestinal tract where these parasites infect. In contrast, the invasion of sporozoites into host intestinal cells could be significantly inhibited by antibodies targeting EaMIC3, EmMIC3, EmiMIC3, EaMIC3-MAR3, EmMIC3-MAR2, and EmiMIC3-MAR4. Substitution experiments involving MAR domains highlighted the crucial roles of EaMIC3-MAR3, EmMIC3-MAR2, and EmiMIC3-MAR4 in governing interactions with host ligands. Furthermore, animal experiments substantiated the significant contribution of EmiMIC3, EmiMIC3-MAR4, and their polyclonal antibodies in conferring protective immunity to Eimeria-affiliated birds. In summary, EaMIC3, EmMIC3, and EmiMIC3 are the underlying factors behind the diverse tissue tropisms exhibited by E. acervuline, E. maxima, and E. mitis, and EaMIC3-MAR3, EmMIC3-MAR2, and EmiMIC3-MAR4 are the major determinants of MIC-mediated tissue tropism of each parasite. The results illuminated the molecular basis of the modes of action of Eimeria MICs, thereby facilitating an understanding and rationalization of the marked differences in tissue tropisms among E. acervuline, E. maxima, and E. mitis.

Anticoccidial activity of natural plants extracts mixture against Eimeria tenella: An in vitro and in vivo study

Coccidiosis, an acute epidemic intestinal disease of poultry, is caused by the parasitic protozoan genus Eimeria, with Eimeria tenella being the most pathogenic spp. Novel approaches are required to address the limitations of current treatments for this disease. We investigated the effects of eight plant extracts and essential oils and their mixture on Eimeria tenella as potential treatments for coccidial infection. The anticoccidial effects of non-toxic concentrations of Punica granatum L. (0.005 mg/mL), Plantago asiatica L. (0.780 mg/mL), Bidens pilosa L. (0.390 mg/mL), Acalypha australis L. (0.390 mg/mL), Pteris multifida Poir (0.050 mg/mL), and Portulaca oleracea L. sp. Pl. (0.050 mg/mL) extracts; Artemisia argyi Levl. et Vant. (0.010 μL/mL) and Camellia sinensis (L.) O. Ktze (0.050 μL/mL) essential oils; and their mixture (0.500 mL/mL) on Eimeria tenella were determined using cell viability assays, flow cytometry, and in vivo studies. The eight plant extracts and essential oils and their mixture inhibited Eimeria tenella sporozoites from invading chicken embryo fibroblast cells in vitro. The extract and essential oil mixture improved the feed conversion ratio and body weight gain, reduced fecal oocyst excretion, substantially reduced the mortality of Eimeria tenella-infected chickens, and reduced Eimeria tenella-induced cecal damage in vivo. The results suggest that the extract and essential oil mixtures inhibit Eimeria tenella invasion both in vitro and in vivo, demonstrating their potential as anticoccidial agents.

Preliminary evaluation of the protective effects of recombinant AMA1 and IMP1 against Eimeria stiedae infection in rabbits

BACKGROUND

Eimeria stiedae parasitizes the bile duct, causing hepatic coccidiosis in rabbits. Coccidiosis control using anticoccidials led to drug resistance and residues; therefore, vaccines are required as an alternative control strategy. Apical membrane antigen 1 (AMA1) and immune mapped protein 1 (IMP1) are surface-located proteins that might contribute to host cell invasion, having potential as candidate vaccine antigens.

METHODS

Herein, we cloned and expressed the E. stiedae EsAMA1 and EsIMP1 genes. The reactogenicity of recombinant AMA1 (rEsAMA1) and IMP1 (rEsIMP1) proteins were investigated using immunoblotting. For the vaccination-infection trial, rabbits were vaccinated with rEsAMA1 and rEsIMP1 (both 100 μg/rabbit) twice at 2-week intervals. After vaccination, various serum cytokines were measured. The protective effects of rEsAMA1 and rEsIMP1 against E. stiedae infection were assessed using several indicators. Sera were collected weekly to detect the specific antibody levels.

RESULTS

Both rEsAMA1 and rEsIMP1 showed strong reactogenicity. Rabbits vaccinated with rEsAMA1 and rEsIMP1 displayed significantly increased serum IL-2 (F _{(4, 25)} = 9.53, P = 0.000), IL-4 (F _{(4, 25)} = 7.81, P = 0.000), IL-17 (F _{(4, 25)} = 8.55, P = 0.000), and IFN-γ (F _{(4, 25)} = 6.89, P = 0.001) levels; in the rEsIMP1 group, serum TGF-β1 level was also elevated (F _{(4, 25)} = 3.01, P = 0.037). After vaccination, the specific antibody levels increased and were maintained at a high level. The vaccination-infection trial showed that compared with the positive control groups, rabbits vaccinated with the recombinant proteins showed significantly reduced oocyst output (F _{(5, 54)} = 187.87, P = 0.000), liver index (F _{(5, 54)} = 37.52, P = 0.000), and feed conversion ratio; body weight gain was significantly improved (F _{(5, 54)} = 28.82, P = 0.000).

CONCLUSIONS

rEsAMA1 and rEsIMP1 could induce cellular and humoral immunity, protecting against E. stiedae infection. Thus, rEsAMA1 and rEsIMP1 are potential vaccine candidates against E. stiedae.

Combined oral immunization with probiotics Entercoccus faecalis delivering surface-anchored Eimeria tenella proteins provide protective efficacies against homologous infection in chickens

Background and Objectives

Avian coccidiosis is an intestinal parasitic disease exerting a highly negative impact on the global poultry industry. The aim of the present study is to evaluate the immune protective efficacies against Eimeria tenella infection in chickens orally immunized with combined recombinant probiotics Entercoccus faecalis (E. faecalis) delivering surface-anchored E. tenella proteins.

Methods

Four kinds of novel probiotics vaccines that surface-expressing four Eimeria tenella (E. tenella) proteins EtAMA1, EtIMP1, EtMIC2 and Et3-1E were produced, respectively. The expression of four target proteins on the surface of recombinant bacteria was detected by Western blot and indirect immunofluorescence assay (IFA). Then the four kinds of recombinant E. faecalis were combined to immunize chickens via oral route in different combinations. The immunizations were performed three times at two-week intervals, and each for three consecutive days. After immunizations, chickens in each immunized group were orally challenged with E. tenella sporulated oocysts. The immune responses and protective efficacies against homologous infection were evaluated.

Results

The results showed that three or four live recombinant E. faecalis induced effective antigen-specific humoral, intestinal mucosal immune responses, stimulated peripheral T lymphocytes proliferation, and displayed partial protections against homologous challenge as measured by cecal lesions, oocyst shedding, and body weight gain (BWG). Notably, higher levels of protective efficacies were observed when the four recombinant E. faecalis delivering target proteins were combined.

Conclusion

Chickens orally administrated with three or four, especially the four combined recombinant E. faecalis stimulated specific immune responses, which provided anti-coccidial effects. This study offers an idea for future development of novel vaccines based on multi-antigens delivered by probiotic bacteria.

Characterization of vaccine-induced immune responses against coccidiosis in broiler chickens

Coccidiosis, caused by Eimeria protozoan species, is an economically important enteric disease of poultry. Although commercial live vaccines are widely used for disease control, the vaccine-induced protective immune mechanisms are poorly characterized. The present study used a commercial broiler vaccine containing a mixture of E. acervulina, E. maxima, and E. tenella. One-day-old chicks were vaccinated by spray followed by a challenge at 21 days of age with a mixture of wild type Eimeria species via oral gavage. Oocyst shedding, immune gene expression and cellular responses in the spleen and cecal tonsils were measured at pre- (days 14 and 21) and post-challenge (days 24, 28 and 35) time points. Results showed that the oocyst counts were significantly reduced in the vaccinated chickens at post-challenge compared to unvaccinated control group. While the vaccinated birds had a significantly increased toll-like receptor (TLR) 21 gene expression at pre-challenge, the transcription of interferon (IFN)γ, Interleukin (IL)-12 and CD40 genes in spleen and cecal tonsils of these birds was significantly higher at post-challenge compared to unvaccinated chickens. Cellular immunophenotyping analysis found that vaccination led to increased frequency of macrophages and activated T cells (CD8⁺CD44⁺ and CD4⁺CD44⁺) in the spleen and cecal tonsils at post-challenge. Furthermore, in vitro stimulation of chicken macrophages (MQ-NCSU cells) with purified individual species of E. acervulina, E. maxima, and E. tenella showed a significantly increased expression of TLR21, TLR2 and IFNγ genes as well as nitric oxide production. Collectively, these findings suggest that TLR21 and TLR2 may be involved in the immune cell recognition of Eimeria parasites and that the vaccine can induce a robust macrophage activation leading to a T helper-1 dominated protective response at both local and systemic lymphoid tissues.

Molecular characterization of glyceraldehyde-3-phosphate dehydrogenase from Eimeria tenella

Chicken coccidiosis is an extremely common and lethally epidemic disease caused by Eimeria spp. The control measures of coccidiosis depend mainly on drugs. However, the ensuing drug resistance problem has brought considerable economic loss to the poultry industry. In our previous study, comparative transcriptome analyses of a drug-sensitive (DS) strain and two drug-resistant strains (diclazuril-resistant (DZR) and maduramicin-resistant (MRR) strains) of Eimeria tenella were carried out by transcriptome sequencing. The expression of glyceraldehyde-3-phosphate dehydrogenase of E. tenella (EtGAPDH) was upregulated in the two resistant strains. In this study, we cloned and characterized EtGAPDH. Indirect immunofluorescence localization was used to observe the distribution of EtGAPDH in E. tenella. The results showed that the protein was distributed mainly on the surface of sporozoites and merozoites, and in the cytoplasm of merozoites. qPCR was performed to detect the transcription level of EtGAPDH in the different developmental stages of the E. tenella DS strain. The transcription level of EtGAPDH was significantly higher in second-generation merozoites than in the other three stages. The transcription level of EtGAPDH in the different drug-resistant strains and DS strain of E. tenella was also analyzed by qPCR. The results showed that the transcription level was significantly higher in the two drug-resistant strains (MRR and DZR) than in the DS strain. As the concentration of diclazuril and maduramicin increased, the transcription levels also increased. Western blot results showed that EtGAPDH protein was upregulated in the DZR and MRR strains. Enzyme activity showed that the enzyme activity of EtGAPDH was higher in the two resistant strains than in the DS strain. These results showed that EtGAPDH possess several roles that separate and distinct from its glycolytic function and maybe involved in the development of E. tenella resistance to anticoccidial drugs.

Molecular characterization and immune protection by cystathionine β-synthase from Eimeria tenella

Eimeria tenella is an obligate intracellular apicomplexan parasite that causes avian coccidiosis and leads to severe economic losses in the global poultry industry. Cystathionine β-synthase (CBS) and cystathionine γ-lyase (CGL) act together to generate H2S in the reverse transsulfuration pathway. In this study, E. tenella Cystathionine β-synthase (EtCBS) was cloned using rapid amplification of cDNA 5'-ends (5'RACE) and characterized, and its immunoprotective effects were evaluated. The recombinant EtCBS protein (rEtCBS) was expressed and successfully recognized by anti-sporozoites (Spz) protein rabbit serum. EtCBS mRNA levels were highest in Spz by qPCR, and the protein expression levels were higher in unsporulated oocysts (UO) than in other stages by Western blot. Indirect immunofluorescence showed that EtCBS protein was found on the surface of Spz and second-generation merozoites (Mrz). The invasion inhibition assays showed that rabbit anti-rEtCBS polyclonal antibodies effectively inhibited parasite invasion host cells. Chickens immunized with rEtCBS protein showed prominently increased weight gains and decreased oocyst output compared to nonimmunized and infected control group. The results suggest that EtCBS could be a potential vaccine candidate against E. tenella.

A bivalent vaccine against avian necrotic enteritis and coccidiosis

AIMS

In this study, we attempted to design a recombinant vaccine harbouring domain with a key role in enterocyte attachment and cell invasion in necrotic enteritis (NE) and coccidiosis.

METHODS AND RESULTS

In this study, we investigated whether a recombinant protein consisting of necrotic enteritis B-like toxin, C-terminal domain of alpha-toxin, apical membrane antigen 1 (AMA1), and Rhoptry neck protein 2 (RON2) which we call "NeCoVac" hereafter, can improve protection against both diseases compared to vaccination with each antigen in previous studies. Birds intestinal lesion scores and specific antibody levels were measured to determine protection after oral gavage challenges with virulent Clostridium perfringens and LIVACOX^® T. Birds immunized with NeCoVac were protected up to 84% against NE and coccidiosis compared to unimmunized and even positive groups (groups treated with LIVACOX^® T [coccidiosis live vaccine] and tylosin as routine veterinary interventions) (p < 0.05).

CONCLUSIONS

Our findings suggest that vaccination with NeCoVac is highly efficient in protecting birds from NE, coccidiosis and a combination of both diseases.

SIGNIFICANCE AND IMPACT OF THE STUDY

The present study is the first one to describe the combinatorial use of AMA1 and RON2 against coccidiosis, and the first report using NeCoVac against NE and coccidiosis together.

Curcumin reduces enteric isoprostane 8-iso-PGF2α and prostaglandin GF2α in specific pathogen-free Leghorn chickens challenged with Eimeria maxima

The purpose of this pilot study was to evaluate and determine the concentration of prostaglandin GF2α (PGF2α) and isoprostane 8‐iso‐PGF2α in plasma and intestine of specific pathogen-free (SPF) Leghorn chickens challenged with Eimeria maxima, with or without dietary supplementation of curcumin using solid‐phase microextraction and ultra‐performance liquid chromatography/tandem mass spectrometry. Eighty 1-day-old male SPF chickens were randomly allocated to one of four groups with four replicates (n = 5 chickens/replicate). Groups consisted of: (1) Control (no challenge), (2) Curcumin (no challenge), (3) Eimeria maxima (challenge), and (4) Eimeria maxima (challenge) + curcumin. At day 28 of age, all chickens in the challenge groups were orally gavaged with 40,000 sporulated E. maxima oocysts. No significant differences (P > 0.05) were observed in the groups regardless of the treatment or challenge with E. maxima. Enteric levels of both isoprostane 8‐iso‐PGF2α and PGF2α at 7 days and 9 days post-challenge were significantly increased (P < 0.01) compared to the non-challenge control chickens. Interestingly, the enteric levels of both isoprostane 8‐iso‐PGF2α and PGF2α at 7 days post-challenge were significantly reduced in chickens fed curcumin, compared to control chickens challenge with E. maxima. At 9 days post-challenge, only levels of isoprostane 8‐iso‐PGF2α in the enteric samples were significantly reduced in chickens challenged with E. maxima supplemented with curcumin, compared with E. maxima challenge chickens. No differences of isoprostane 8‐iso‐PGF2α or PGF2α were observed in plasma at both days of evaluation. Similarly, no significant differences were observed between the challenge control or chickens challenge with E. maxima and supplemented with curcumin at both times of evaluation. The results of this pilot study suggests that the antioxidant anti-inflammatory properties of curcumin reduced the oxidative damage and subsequent intestinal mucosal over-production of lipid oxidation products. Further studies to confirm and extend these results in broiler chickens are required.

Identification and Characterization of the ATG8, a Marker of Eimeria tenella Autophagy

Autophagy plays an important role in maintaining cell homeostasis through degradation of denatured proteins and other biological macromolecules. In recent years, many researchers focus on mechanism of autophagy in apicomplexan parasites, but little was known about this process in avian coccidia. In our present study. The cloning, sequencing and characterization of autophagy-related gene (Etatg8) were investigated by quantitative real-time PCR (RT-qPCR), western blotting (WB), indirect immunofluorescence assays (IFAs) and transmission electron microscopy (TEM), respectively. The results have shown 375-bp ORF of Etatg8, encoding a protein of 124 amino acids in E. tenella, the protein structure and properties are similar to other apicomplexan parasites. RT-qPCR revealed Etatg8 gene expression during four developmental stages in E. tenella, but their transcriptional levels were significantly higher at the unsporulated oocysts stage. WB and IFA showed that EtATG8 was lipidated to bind the autophagosome membrane under starvation or rapamycin conditions, and aggregated in the cytoplasm of sporozoites and merozoites, however, the process of autophagosome membrane production can be inhibited by 3-methyladenine. In conclusion, we found that E. tenella has a conserved autophagy mechanism like other apicomplexan parasites, and EtATG8 can be used as a marker for future research on autophagy targeting avian coccidia.

Analysis of Genetic Diversity in Indian Isolates of Rhipicephalus microplus Based on Bm86 Gene Sequence

The control of cattle tick, Rhipicephalus microplus, is focused on repeated use of acaricides. However, due to growing acaricide resistance and residues problem, immunization of animals along with limited use of effective acaricides is considered a suitable option for the control of tick infestations. To date, more than fifty vaccine candidates have been identified and tested worldwide, but two vaccines were developed using the extensively studied candidate, Bm86. The main reason for limited vaccine commercialization in other countries is genetic diversity in the Bm86 gene leading to considerable variation in vaccine efficacy. India, with 193.46 million cattle population distributed in 28 states and 9 union territories, is suffering from multiple tick infestation dominated by R. microplus. As R. microplus has developed multi-acaricide resistance, an efficacious vaccine may provide a sustainable intervention for tick control. Preliminary experiments revealed that the presently available commercial vaccine based on the BM86 gene is not efficacious against Indian strain. In concert with the principle of reverse vaccinology, genetic polymorphism of the Bm86 gene within Indian isolates of R. microplus was studied. A 578 bp conserved nucleotide sequences of Bm86 from 65 R. microplus isolates collected from 9 Indian states was sequenced and revealed 95.6-99.8% and 93.2-99.5% identity in nucleotides and amino acids sequences, respectively. The identities of nucleotides and deduced amino acids were 94.7-99.8% and 91.8-99.5%, respectively, between full-length sequence (orf) of the Bm86 gene of IVRI-I strain and published sequences of vaccine strains. Six nucleotides deletion were observed in Indian Bm86 sequences. Four B-cell epitopes (D519-K554, H563-Q587, C598-T606, T609-K623), which are present in the conserved region of the IVRI-I Bm86 sequence, were selected. The results confirm that the use of available commercial Bm86 vaccines is not a suitable option against Indian isolates of R. microplus. A country-specific multi-epitope Bm86 vaccine consisting of four specific B-cell epitopes along with candidate molecules, subolesin and tropomyosin in chimeric/co-immunization format may provide a sustainable option for implementation in an integrated tick management system.

Molecular characterization and functional analysis of Eimeria tenella citrate synthase

Chicken coccidiosis, caused by an obligate intracellular protozoan parasite of the genus Eimeria, is a major parasitic disease in the intensively reared poultry industry. Due to the widespread use of anticoccidial drugs, resistance has become an inevitable problem. In our previous study, Eimeria tenella citrate synthase (EtCS) was found to be up-expressed in two drug-resistant strains (diclazuril-resistant and maduramycin-resistant strains) compared to drug-sensitive strain by RNA sequence. In this study, we cloned and expressed EtCS and obtain its polyclonal antibodies. Quantitative real-time polymerase chain (qPCR) reactions and Western blots were used to analyze the transcription and translation levels of EtCS in sensitive and three drug-resistant strains. Compared with the sensitive strain, the transcription of EtCS was both significantly upregulated in diclazuril-resistant and maduramycin-resistant strains, but was not significantly different in salinomycin-resistant strain. No significant difference was seen in translation level in the three drug-resistant strains. Indirect immunofluorescence indicated that EtCS was mainly located in the cytoplasm of sporozoites except for posterior refractile bodies and in the cytoplasm and surface of merozoites. Anti-rEtCS antibody has inhibitory effects on E. tenella sporozoite invasion of DF-1 cells and the inhibition rate is more than 83%. Binding of the protein to chicken macrophage (HD11) cells was confirmed by immunofluorescence assays. When macrophages were treated with rEtCS, secretion of nitric oxide and cell proliferation of the macrophages were substantially reduced. These results showed that EtCS may be related to host cell invasion of E. tenella and involve in the development of E.tenella resistance to some drugs.

Eimeria tenella Translation Initiation Factor eIF-5A That Interacts With Calcium-Dependent Protein Kinase 4 Is Involved in Host Cell Invasion

Eimeria tenella is an apicomplexan, parasitic protozoan known to infect poultry worldwide. An important calcium-dependent protein kinase (CDPK) has been identified in plants, green algae, ciliates and apicomplexan, such as E. tenella. CDPKs are effector molecules involved in calcium signaling pathways, which control important physiological processes such as gliding motility, reproduction, and host cell invasion. Given that CDPKs are not found in the host, studying the functions of CDPKs in E. tenella may serve as a basis for developing new therapeutic drugs and vaccines. To assess the function of CDPK4 in E. tenella (EtCDPK4), a putative interactor, translation initiation factor eIF-5A (EteIF-5A), was screened by both co-immunoprecipitation (co-IP) and His pull-down assays followed by mass spectrometry. The interaction between EteIF-5A and EtCDPK4 was determined by bimolecular fluorescence complementation (BiFC), GST pull-down, and co-IP. The molecular characteristics of EteIF-5A were then analyzed. Quantitative real-time polymerase chain reaction and western blotting were used to determine the transcription and protein levels of EteIF-5A in the different developmental stages of E. tenella. The results showed that the transcription level of EteIF-5A mRNA was highest in second-generation merozoites, and the protein expression level was highest in unsporulated oocysts. Indirect immunofluorescence showed that the EteIF-5A protein was found throughout the cytoplasm of sporozoites, but not in the refractile body. As the invasion of DF-1 cells progressed, EteIF-5A fluorescence intensity increased in trophozoites, decreased in immature schizonts, and increased in mature schizonts. The secretion assay results, analyzed by western blotting, indicated that EteIF-5A was a secreted protein but not from micronemes. The results of invasion inhibition assays showed that rabbit anti-rEteIF-5A polyclonal antibodies effectively inhibited cell invasion by sporozoites, with an inhibition rate of 48%.

Identification and Characterization of a Novel Apical Membrane Antigen 3 in Eimeria tenella

Eimeria tenella is an obligate intracellular parasite in the phylum Apicomplexa. As described for other members of Apicomplexa, apical membrane antigen 1 (AMA1) has been shown to be critical for sporozoite invasion of host cells by E. tenella. Recently, an E. tenella paralogue of AMA1 (EtAMA1), dubbed sporoAMA1 (EtAMA3), was identified in proteomic and transcriptomic analyses of E. tenella, but not further characterized. Here, we show that EtAMA3 is a type I integral membrane protein that has 24% -38% identity with other EtAMAs. EtAMA3 has the same pattern of Cys residues in domains I and II of AMA1 orthologs from apicomplexan parasites, but high variance in domain III, with all six invariant Cys residues absent. EtAMA3 expression was developmentally regulated at the mRNA and protein levels. EtAMA3 protein was detected in sporulated oocysts and sporozoites, but not in the unsporulated oocysts or second-generation merozoites. EtAMA3 is secreted by micronemes and is primarily localized to the apical end of sporozoites during host-cell invasion. Additionally, pretreatment of sporozoites with rEtAMA3-specific antibodies substantially impeded their invasion into host cells. These results suggest EtAMA3 is a sporozoite-specific protein that is involved in host-cell sporozoite invasion.

Further investigation of the characteristics and biological function of Eimeria tenella apical membrane antigen 1

Apical membrane antigen 1 (AMA1) is a type I integral membrane protein that is highly conserved in apicomplexan parasites. Previous studies have shown that Eimeria tenella AMA1 (EtAMA1) is critical for sporozoite invasion of host cells. Here, we show that EtAMA1 is a microneme protein secreted by sporozoites, confirming previous results. Individual and combined treatment with antibodies of EtAMA1 and its interacting proteins, E. tenella rhoptry neck protein 2 (EtRON2) and Eimeria-specific protein (EtESP), elicited significant anti-invasion effects on the parasite in a concentration-dependent manner. The overexpression of EtAMA1 in DF-1 cells showed a significant increase of sporozoite invasion. Isobaric tags for relative and absolute quantitation (iTRAQ) coupled with LC-MS/MS were used to screen differentially expressed proteins (DEPs) in DF-1 cells transiently transfected with EtAMA1. In total, 3953 distinct nonredundant proteins were identified and 163 of these were found to be differentially expressed, including 91 upregulated proteins and 72 downregulated proteins. The DEPs were mainly localized within the cytoplasm and were involved in protein binding and poly(A)-RNA binding. KEEG analyses suggested that the key pathways that the DEPs belonged to included melanogenesis, spliceosomes, tight junctions, and the FoxO and MAPK signaling pathways. The data in this study not only provide a comprehensive dataset for the overall protein changes caused by EtAMA1 expression, but also shed light on EtAMA1’s potential molecular mechanisms during Eimeria infections.

Eimeria tenella Eimeria-specific protein that interacts with apical membrane antigen 1 (EtAMA1) is involved in host cell invasion

Background

Avian coccidiosis is a widespread, economically significant disease of poultry, caused by several Eimeria species. These parasites have complex and diverse life-cycles that require invasion of their host cells. This is mediated by various proteins secreted from apical secretory organelles. Apical membrane antigen 1 (AMA1), which is released from micronemes and is conserved across all apicomplexans, plays a central role in the host cell invasion. In a previous study, some putative EtAMA1-interacting proteins of E. tenella were screened. In this study, we characterized one putative EtAMA1-interacting protein, E. tenella Eimeria -specific protein (EtEsp).

Methods

Bimolecular fluorescence complementation (BiFC) and glutathione S-transferase (GST) fusion protein pull-down (GST pull-down) were used to confirm the interaction between EtAMA1 and EtEsp in vivo and in vitro. The expression of EtEsp was analyzed in different developmental stages of E. tenella with quantitative PCR and western blotting. The secretion of EtEsp protein was tested with staurosporine when sporozoites were incubated in complete medium at 41 °C. The localization of EtEsp was analyzed with an immunofluorescence assay (IFA). An in vitro invasion inhibition assay was conducted to assess the ability of antibodies against EtEsp to inhibit cell invasion by E. tenella sporozoites.

Results

The interaction between EtAMA1 and EtEsp was confirmed with BiFC and by GST pull-down. Our results show that EtEsp is differentially expressed during distinct phases of the parasite life-cycle. IFA showed that the EtEsp protein is mainly distributed on the parasite surface, and that the expression of this protein increases during the development of the parasite in the host cells. Using staurosporine, we showed that EtEsp is a secreted protein, but not from micronemes. In inhibition tests, a polyclonal anti-rEtEsp antibody attenuated the capacity of E. tenella to invade host cells.

Conclusion

In this study, we show that EtEsp interacts with EtAMA1 and that the protein is secreted protein, but not from micronemes. The protein participates in sporozoite invasion of host cells and is maybe involved in the growth of the parasite. These data have implications for the use of EtAMA1 or EtAMA1-interacting proteins as targets in intervention strategies against avian coccidiosis.

Transgenic Eimeria parasite: A potential control strategy for chicken coccidiosis

Poultry industry has been very instrumental in curtailing malnutrition and poverty and as such contributing to economic growth. However, production loss in poultry industry due to parasitic disease such as coccidiosis has become a global challenge. Chicken coccidiosis is an enteric disease that is associated with morbidity and mortality. The control of this parasite through anticoccidial live vaccines and drugs has been very successful though with some limitations such as the cost of production of live vaccines, and drugs resistance which is a public health concern. The discovery of Eimeria vaccine antigens such as Apical membrane antigens (AMA)-1 and Immune mapped protein (IMP)-1 have introduced the use of recombinant vaccines as alternative control measures against chicken coccidiosis. Although some protections have been reported among recombinant vaccines, improving their protective efficacy has triggered the search for a novel and efficient delivery vehicle. Transgenic Eimeria, which is constructed either through stable or transient transfection is currently being explored as novel delivery vehicle of Eimeria vaccine antigens. Due to partial protections reported in chickens vaccinated with transgenic Eimeria lines expressing different Eimeria antigens, improving protective efficacy becomes imperative. Recent trends in the design of transgenic Eimeria for potential application in the control of chicken coccidiosis are summarized in this review. We conclude that, with improved protective efficacy using multiple vaccine antigens, transgenic Eimeria parasite could fill the gap in the control of chicken coccidiosis as an efficient anticoccidial vaccine.

Protective effects of a food-grade recombinant Lactobacillus plantarum with surface displayed AMA1 and EtMIC2 proteins of Eimeria tenella in broiler chickens

Background

Avian coccidiosis posts a severe threat to poultry production. In addition to commercial attenuated vaccines, other strategies to combat coccidiosis are urgently needed. Lactobacillus plantarum has been frequently used for expression of foreign proteins as an oral vaccine delivery system using traditional erythromycin resistance gene (erm). However, antibiotic selection markers were often used during protein expression and they pose a risk of transferring antibiotic resistance genes to the environment, and significantly restricting the application in field production. Therefore, a food-grade recombinant L. plantarum vaccine candidate would dramatically improve its application potential in the poultry industry.

Results

In this study, we firstly replaced the erythromycin resistance gene (erm) of the pLp_1261Inv-derived expression vector with a non-antibiotic, asd-alr fusion gene, yielding a series of non-antibiotic and reliable, food grade expression vectors. In addition, we designed a dual-expression vector that displayed two foreign proteins on the surface of L. plantarum using the anchoring sequences from either a truncated poly-γ-glutamic acid synthetase A (pgsA′) from Bacillus subtilis or the L. acidophilus surface layer protein (SlpA). EGFP and mCherry were used as marker proteins to evaluate the surface displayed properties of recombinant L. plantarum strains and were inspected by western blot, flow cytometry and fluorescence microscopy. To further determine its application as oral vaccine candidate, the AMA1 and EtMIC2 genes of E. tenella were anchored on the surface of L. plantarum strain. After oral immunization in chickens, the recombinant L. plantarum strain was able to induce antigen specific humoral, mucosal, and T cell-mediated immune responses, providing efficient protection against coccidiosis challenge.

Conclusions

The novel constructed food grade recombinant L. plantarum strain with double surface displayed antigens provides a potential efficient oral vaccine candidate for coccidiosis.

Eimeria tenella: specific EtAMA1-binding peptides inhibit sporozoite entry into host cells

Avian coccidiosis caused by Eimeria inflicts high economic losses to the poultry industry. Application of drugs and live vaccines presents particular challenges in pathogen resistance and cost, hence alternative anti-coccidial strategies are needed. In this study, peptides that specifically bind E. tenella AMA1 (EtAMA1) were screened from a phage display peptide library. The positive clones of target phages were characterized by ELISA after four rounds of biopanning. The binding capabilities with EtAMA1 and sporozoite proteins for the two selected peptides were detected by ELISA. The role of the two target peptides in inhibiting sporozoite invasion of MDBK cells was evaluated in vitro and the anti-coccidial effects of the two phages were assessed by an animal experiment. The three-dimensional (3D) structural model of EtAMA1 extracellular domain (EctoAMA1) protein was constructed based on the crystal template of TgAMA1 (PDB ID: 2 × 2Z), and the molecular docking between target peptides and EctoAMA1 model was analyzed. The results showed that two selected phages strongly interacted with EctoAMA1 and sporozoites protein. Two corresponding specific EtAMA1-binding peptide (named L and C) showed significant effects on inhibiting sporozoite invasion of MDBK cells. Chickens orally fed the two target phages showed partial protection against homologous challenge. Homology modeling analysis showed an apical hydrophobic groove was shaped on the top of the EctoAMA1 model. Molecular docking indicated the interaction between the EctoAMA1 protein and the two peptides, which was mainly reflected by the hydrophobic interaction and formation of intermolecular hydrogen bond. The above results suggest that the peptides L and C, especially L peptide, competed with E. tenella rhotry neck protein 2 (EtRON2) for binding to EtAMA1 located on the surface of sporozoites, and therefore inhibited the parasite invasion into cells.

Effects of host fatty acid-binding protein 4 on Eimeria tenella sporozoites invasion of cells

In our previous study, proteomics analyses of host cells infected with Eimeria tenella sporozoites coupled with isobaric tags for relative and absolute quantitation, identified several host proteins related to Eimeria invasion. In this study, A 458-bp Gallus gallus fatty acid-binding protein 4 (FABP4) gene was cloned and subcloned to pET-28c(+) vector to construct the prokaryotic recombinant expression plasmid pET-28c(+)-FABP4. The 18.5 kDa recombinant FABP4 protein (rFABP4) was expressed and identified by western blotting. Expression of FABP4 in E. tenella sporozoite-infected DF-1 cells was downregulated significantly than in non-infected cells detected by western blotting and immunohistochemistry. The antibody inhibition assay showed that antibodies against FABP4 at 50, 100, 200, 300, and 400 μg/mL had no significant effect on sporozoite invasion. BMS-309403 and transforming growth factor-β3 (TGF-β3) was used to inhibit and improve the expression of FABP4 in DF-1 cells, respectively, and their effect on the sporozoite invasion of cells was detected by flow cytometry. Sporozoite invasion rate in the BMS-309403-treated group was not significantly affected; however, the invasion rate in the TGF-β3-treated group declined significantly. These results show that host FABP4 plays a negative role in Eimeria invasion. However, further studies are needed to elucidate the exact mechanism of how FABP4 negatively regulates Eimeria invasion.

The effect of autophagy on the survival and invasive activity of Eimeria tenella sporozoites

Autophagy is a cellular process that is vital for the maintenance of homeostasis in eukaryotic cells. Currently, autophagy-related genes (atgs) in the Eimeria tenella genome database have been reported, but very little is known about the effects of autophagy on the survival and invasive activity of this protozoan. In this study, we investigated the autophagy in E. tenella sporozoites under starvation and autophagy-modulators treatments and evaluated the autophagy influence on cellular adenosine triphosphate (ATP) levels, the survival rate and the invasive activity of the sporozoites. The results showed that the autophagy could be induced in the sporozoites by starvation or inducer rapamycin (RP), but it could be inhibited by 3-methyladenine (3-MA) treatment. The sporozoites after starvation and RP-treatment displayed punctate signals of EtATG8 and formed autophagosomes. The survival rate of the sporozoites under starvation was significantly lower than that in the control group, whereas the ATP levels in sporozoite were far greater than those in the control. The quantitative real-time reverse transcriptase polymerase chain reaction (qRT-PCR) showed that the invasive activity of the sporozoites was up- and down-regulated by RP and 3-MA induction, respectively. Our results indicate that autophagy has effects on the survival and invasive activity of E. tenella sporozoites, which may provide new insights into anti-coccidial drugs.

Diagnosis and control of chicken coccidiosis: a recent update

Coccidiosis is a deadly disease that hampers chicken's productivity and welfare. Thus, the disease is a major menace to the global poultry industry. Coccidiosis which is caused by the apicomplexan parasite of the genus Eimeria has seven known species which affect the different parts of the intestinal tract of chickens. The disease which occurs by ingestion of sporulated oocyst has been associated with poor poultry management system. Mixed infection among the species of this parasite contributes to both pathogenicity and misdiagnosis of the disease. A progress in identification and diagnosis approach which cuts across pathological, morphological and molecular has been reported for this parasite. Control measures which include anticoccidial drugs, vaccines and natural products have dominated literature for this disease. However, the emergence of genetic and antigenic diversity with implication on resistance to anticoccidials among different strains of Eimeria parasite has generated concerns on the effectiveness of the current anticoccidial vaccines. A new look on the control strategy therefore becomes imperative. This study reviews the current trends on the identification and control of chicken coccidiosis with focus on (1) Avian coccidiosis (2) Epidemiology of chicken coccidiosis (3) Eimeria parasite and distribution in poultry (4) Diagnosis of Eimeria parasite (5) Control measures of coccidiosis (6) Threats posed by genetic and antigenic diversity of Eimeria parasite on coccidiosis control. Genomic study on diversity of Eimeria parasite becomes imperative for effective vaccine design against coccidiosis.

Molecular characterization and protective efficacy of the microneme 2 protein from Eimeria tenella

Microneme proteins play an important role in the adherence of apicomplexan parasites to host cells during the invasion process. In this study, the microneme 2 protein from the protozoan parasite Eimeria tenella (EtMIC2) was cloned, characterized, and its protective efficacy as a DNA vaccine investigated. The EtMIC2 gene, which codes for a 35.07 kDa protein in E. tenella sporulated oocysts, was cloned and recombinant EtMIC2 protein (rEtMIC2) was produced in an Escherichia coli expression system. Immunostaining with an anti-rEtMIC2 antibody showed that the EtMIC2 protein mainly localized in the anterior region and membrane of sporozoites, in the cytoplasm of first- and second-generation merozoites, and was strongly expressed during first-stage schizogony. In addition, incubation with specific antibodies against EtMIC2 was found to efficiently reduce the ability of E. tenella sporozoites to invade host cells. Furthermore, animal-challenge experiments demonstrated that immunization with pcDNA3.1(+)-EtMIC2 significantly increased average body weight gain, while decreasing the mean lesion score and oocyst output in chickens. Taken together, these results suggest that EtMIC2 plays an important role in parasite cell invasion and may be a viable candidate for the development of new vaccines against E. tenella infection in chickens.

Recombinant lactococcus lactis expressing Eimeria tenella AMA1 protein and its immunological effects against homologous challenge

Avian coccidiosis leads to severe economic losses for the global poultry industry. Apical membrane antigen 1 (AMA1) of E. tenella (EtAMA1) plays a vital role during invasion of parasites into host cells. In the present study, recombinant live Lactococcus lactis expressing cytoplasmic, secreted and cell wall-anchored EtAMA1 protein were respectively constructed. The three live bacteria were respectively administered orally to SPF chickens (100 μl bacteria containing 5 × 10⁹ CFU per chicken) for three times at 10-day intervals. After immunization, the lymphocyte proliferative function, the percentage of CD4⁺ and CD8α⁺ T cells in peripheral blood, and the IgG titers in serum of chickens in each group were respectively measured. The protective effects of live bacteria expressing EtAMA1 protein against E. tenella challenge were evaluated based on body weight gain (BWG), lesion score in cecum, oocyst descrease ratio. The results showed that chickens immunized with three live bacteria, especially the bacteria expressing cell wall-anchored EtAMA1 protein, displayed higher IgG titers and CD4⁺ T cells proportions, thus provided more immune protective effects against homologous challenge compared with the PBS control group and vector control group (lactococci harboring pTX8048). The oocyst decrease ratio of 33.33% from chickens immunized with lactococci expressing cell wall-anchored EctoAMA1 was observed, which was higher than that of 27.67% and 25.37% from the other two bacteria-immunized groups, respectively. The above results suggested that cell wall-anchored EtAMA1 protein delivered by Lactococcus lactis could stimulate an effective immune responses against Eimeria infection.

Molecular characterization and functional analysis of Eimeria tenella malate dehydrogenase

Eimeria tenella is a serious intracellular parasite that actively invades cecal epithelial cells of chickens. The widespread use of drugs causes severe resistance to Eimeria tenella. We detected that malate dehydrogenase (MDH), one of the differentially expressed genes, was upregulated in diclazuril-resistant and maduramicin-resistant strains through transcriptome sequencing. In this study, we cloned and expressed MDH of E. tenella (EtMDH). Quantitative real-time polymerase chain reactions (qPCR) and Western blots were used to analyze the expression of EtMDH in resistant and sensitive strains, indicating EtMDH was upregulated in two resistant strains at the messenger RNA and protein levels. Enzyme activity was tested through absorbance measurement and the EtMDH activity increased in two resistant strains. Expression levels of EtMDH in four developmental stages of E. tenella were tested through qPCR and Western blot. Invasion inhibition assays explored if EtMDH was involved in invasion of DF-1 cells by E. tenella sporozoites. Indirect immunofluorescence assays investigated EtMDH distribution during parasite development in DF-1 cells invaded by E. tenella sporozoites. Experimental results showed that EtMDH may be related to drug resistance of E. tenella during its development and invasion. EtMDH may be an effective molecular marker for detection of E. tenella drug resistance.

Construction of Lactococcus lactis expressing secreted and anchored Eimeria tenella 3-1E protein and comparison of protective immunity against homologous challenge

Two novel plasmids pTX8048-SP-Δ3-1E and pTX8048-SP-NAΔ3-1E-CWA were constructed. The plasmids were respectively electrotransformed into L. lactis NZ9000 to generate strain of L. lactis/pTX8048-SP-Δ3-1E in which 3-1E protein was expressed in secretion, and L. lactis/pTX8048-SP-NAΔ3-1E-CWA on which 3-1E protein was covalently anchored to the surface of bacteria cells. The expression of target proteins were examined by Western blot. The live lactococci expressing secreted 3-1E protein, anchored 3-1E protein, and cytoplasmic 3-1E protein was administered orally to chickens respectively, and the protective immunity and efficacy were compared by animal experiment. The results showed oral immunization to chickens with recombinant lactococci expressing anchored 3-1E protein elicited high 3-1E-specific serum IgG, increased high proportion of CD4⁺ and CD8α⁺ cells in spleen, alleviated average lesion score in cecum, decreased the oocyst output per chicken compared to lactococci expressing cytoplasmic or secreted 3-1E protein. Taken together, these findings indicated the surface anchored Eimeria protein displayed by L. lacits can induce protective immunity and partial protection against homologous infection.

Molecular Characterization and Functional Analysis of a Novel Calcium-Dependent Protein Kinase 4 from Eimeria tenella

Eimeria tenella is an obligate intracellular parasite that actively invades cecal epithelial cells of chickens. The basis of cell invasion is not completely understood, but some key molecules of host cell invasion have been discovered. This paper investigated the characteristics of calcium-dependent protein kinase 4 (EtCDPK4), a critical molecule in E. tenella invasion of host cells. A full-length EtCDPK4 cDNA was identified from E. tenella using rapid amplification of cDNA ends. EtCDPK4 had an open reading frame of 1803 bp encoding a protein of 600 amino acids. Quantitative real-time PCR and western blotting were used to explore differences in EtCDPK4 transcription and translation in four developmental stages of E. tenella. EtCDPK4 was expressed at higher levels in sporozoites, but translation was higher in second-generation merozoites. In vitro invasion inhibition assays explored whether EtCDPK4 was involved in invasion of DF-1 cells by E. tenella sporozoites. Polyclonal antibodies against recombinant EtCDPK4 (rEtCDPK4) inhibited parasite invasion, decreasing it by approximately 52%. Indirect immunofluorescence assays explored EtCDPK4 distribution during parasite development after E. tenella sporozoite invasion of DF-1 cells in vitro. The results showed that EtCDPK4 might be important in sporozoite invasion and development. To analyze EtCDPK4 functional domains according to the structural characteristics of EtCDPK4 and study the kinase activity of rEtCDPK4, an in vitro phosphorylation system was established. We verified that rEtCDPK4 was a protein kinase that was completely dependent on Ca2+ for enzyme activity. Specific inhibitors of rEtCDPK4 activity were screened by kinase activity in vitro. Some specific inhibitors were applied to assays of DF-1 cell invasion by E. tenella sporozoites to confirm that the inhibitors functioned in vitro. W-7, H-7, H-89, and myristoylated peptide inhibited DF-1 invasion by E. tenella sporozoites. The experimental results showed that EtCDPK4 may be involved in E. tenella invasion of chicken cecal epithelial cells.

Molecular characterization and protective efficacy of silent information regulator 2A from Eimeria tenella

Background

Silent information regulator 2 (SIR2) proteins are a family of NAD + -dependent protein deacetylases that are considered potential targets for anti-parasitic agents. In this study, we cloned and characterized SIR2A of the protozoan parasite Eimeria tenella (EtSIR2A) and investigated its protective efficacy as a DNA vaccine.

Methods

The EtSIR2A gene encoding 33.37 kDa protein from E. tenella second-generation merozoites was cloned, and recombinant EtSIR2A protein (rEtSIR2A) was produced in an Escherichia coli expression system. The rEtSIR2A was used to immunize rabbits. Anti-rEtSIR2A antibodies were used to determine the immunolocolization of EtSIR2A in the parasite by immunofluorescence assay (IFA). Transcript and protein expression of EtSIR2A in different development stages of E. tenella were observed by quantitative real-time PCR (qPCR) and western blot (WB) analysis, respectively. The recombinant plasmid pCAGGS-EtSIR2A was constructed and its efficacy against E. tenella infection in chickens was evaluated.

Results

qPCR and WB analysis revealed EtSIR2A expression was developmentally regulated at both the mRNA and protein levels. EtSIR2A mRNA levels were higher in unsporulated oocysts than at other developmental stages, including sporulated oocysts, sporozoites and second-generation merozoites. In contrast, EtSIR2A protein expression levels were highest in second-generation merozoites, moderate in unsporulated oocysts and sporulated oocysts and lowest in sporozoites. Immunostaining with anti-rEtSIR2A antibody indicated that EtSIR2A was mainly located in the cytoplasm of sporozoites and second-generation merozoites, and was strongly expressed during first stage schizogony. Animal-challenge experiments demonstrated that immunization with pCAGGS-EtSIR2A significantly increased average body-weight gain, and decreased mean lesion score and oocyst output in chickens.

Conclusions

These results suggest that EtSIR2A may play an important role in parasite cell survival and may be an effective candidate for the development of new vaccines against E. tenella infection in chickens.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1871-0) contains supplementary material, which is available to authorized users.

Screening and characterization of apical membrane antigen 1 interacting proteins in Eimeria tenella

Avian coccidiosis is a widespread and economically significant disease of poultry. It is an enteric disease caused by several protozoan Eimeria species. Eimeria belongs to the phylum Apicomplexa, which exhibits an unusual mechanism of host cell invasion. During invasion of host cells, the protein apical membrane antigen 1 (AMA1) is essential for invasion of Toxoplasma gondii and Plasmodium. Contrary to the roles of AMA1 during host cell invasion in T. gondii and Plasmodium, the precise functions of Eimeria AMA1 (EtAMA1) are unclear. In order to study the functions of EtAMA1, a yeast two-hybrid cDNA library was constructed from E. tenella sporozoites. The EtAMA1 ectodomain was cloned into the pGBKT7 vector to construct the bait plasmid pGBKT7- EtAMA1. Autoactivation and toxicity of the bait protein in yeast cells were tested by comparison with the pGBKT7 empty vector. Expression of the bait protein was detected by western blots. The bait plasmid pGBKT7-EtAMA1 was used to screen yeast two-hybrid cDNA library from E. tenella sporozoites. After multiple screenings with high-screening-rate medium and exclusion of false-positive plasmids, positive preys were sequenced and analyzed using BLAST. We obtained 14 putative EtAMA1-interacting proteins including E. tenella acidic microneme protein2 (EtMIC2), E. tenella putative cystathionine beta-synthase, E. tenella Eimeria-specific protein, four E. tenella conserved hypothetical proteins (one in the serine/threonine protein kinase family) and seven unknown proteins. Gene Ontology analysis indicated that two known proteins were associated with metabolic process, pyridoxal phosphate binding and protein phosphorylation. Functional analysis indicated EtMIC2 was implicated in parasite motility, migration, recognition and invasion of host cells. The data suggested that EtAMA1 may be important during host cell invasion, but also involved in other biological processes.

Are Eimeria Genetically Diverse, and Does It Matter?

Eimeria pose a risk to all livestock species as a cause of coccidiosis, reducing productivity and compromising animal welfare. Pressure to reduce drug use in the food chain makes the development of cost-effective vaccines against Eimeria essential. For novel vaccines to be successful, understanding genetic and antigenic diversity in field populations is key. Eimeria species that infect chickens are most significant, with Eimeria tenella among the best studied and most economically important. Genome-wide single nucleotide polymorphism (SNP)-based haplotyping has been used to determine population structure, genotype distribution, and potential for cross-fertilization between E. tenella strains. Here, we discuss recent developments in our understanding of diversity for Eimeria in relation to its specialized life cycle, distribution across the globe, and the challenges posed to vaccine development.

Molecular Characterization and Immune Protection of a New Conserved Hypothetical Protein of Eimeria tenella

The genome sequences of Eimeria tenella have been sequenced, but >70% of these genes are currently categorized as having an unknown function or annotated as conserved hypothetical proteins, and few of them have been studied. In the present study, a conserved hypothetical protein gene of E. tenella, designated EtCHP559, was cloned using rapid amplification of cDNA 5'-ends (5'RACE) based on the expressed sequence tag (EST). The 1746-bp full-length cDNA of EtCHP559 contained a 1224-bp open reading frame (ORF) that encoded a 407-amino acid polypeptide with the predicted molecular weight of 46.04 kDa. Real-time quantitative PCR analysis revealed that EtCHP559 was expressed at higher levels in sporozoites than in the other developmental stages (unsporulated oocysts, sporulated oocysts and second generation merozoites). The ORF was inserted into pCold-TF to produce recombinant EtCHP559. Using western blotting, the recombinant protein was successfully recognized by rabbit serum against E. tenella sporozoites. Immunolocalization by using EtCHP559 antibody showed that EtCHP559 was mainly distributed on the parasite surface in free sporozoites and became concentrated in the anterior region after sporozoites were incubated in complete medium. The EtCHP559 became uniformly dispersed in immature and mature schizonts. Inhibition of EtCHP559 function using anti-rEtCHP559 polyclonal antibody reduced the ability of E. tenella sporozoites to invade host cells by >70%. Animal challenge experiments demonstrated that the recombinant EtCHP559 significantly increased the average body weight gain, reduced the oocyst outputs, alleviated cecal lesions of the infected chickens, and resulted in anticoccidial index >160 against E. tenella. These results suggest that EtCHP559 plays an important role in sporozoite invasion and could be an effective candidate for the development of a new vaccine against E. tenella.

Population, genetic, and antigenic diversity of the apicomplexan Eimeria tenella and their relevance to vaccine development

The phylum Apicomplexa includes serious pathogens of humans and animals. Understanding the distribution and population structure of these protozoan parasites is of fundamental importance to explain disease epidemiology and develop sustainable controls. Predicting the likely efficacy and longevity of subunit vaccines in field populations relies on knowledge of relevant preexisting antigenic diversity, population structure, the likelihood of coinfection by genetically distinct strains, and the efficiency of cross-fertilization. All four of these factors have been investigated for Plasmodium species parasites, revealing both clonal and panmictic population structures with exceptional polymorphism associated with immunoprotective antigens such as apical membrane antigen 1 (AMA1). For the coccidian Toxoplasma gondii only genomic diversity and population structure have been defined in depth so far; for the closely related Eimeria species, all four variables are currently unknown. Using Eimeria tenella, a major cause of the enteric disease coccidiosis, which exerts a profound effect on chicken productivity and welfare, we determined population structure, genotype distribution, and likelihood of cross-fertilization during coinfection and also investigated the extent of naturally occurring antigenic diversity for the E. tenella AMA1 homolog. Using genome-wide Sequenom SNP-based haplotyping, targeted sequencing, and single-cell genotyping, we show that in this coccidian the functionality of EtAMA1 appears to outweigh immune evasion. This result is in direct contrast to the situation in Plasmodium and most likely is underpinned by the biology of the direct and acute coccidian life cycle in the definitive host.

Molecular characterization and functional analysis of subunit 7 of eukaryotic initiation factor 3 from Eimeria tenella

The initiation of translation in eukaryotic cells is stimulated by proteins known as initiation factors (eIFs). A structurally complex eIF composed of multiple subunits, eIF3 has been shown to have various functions in translation in a variety of eukaryotes. Until now, little is known about eIF3 in Eimeria tenella. Based on a previously identified expressed sequence tag(EST), we cloned the eIF3 subunit 7 gene (EteIF3s7) from E. tenella by rapid amplification of the cDNA ends(RACE). The 2278-bp full-length complementary DNA of EteIF3s7 contained a 1716-bp open reading frame (ORF) that encoded a 571-amino acid (aa) polypeptide. The EteIF3s7 protein contained the subunit 7 domain that is characteristic of members of the eIF3 zeta superfamily. The levels of EteIF3s7 messenger RNA and protein were higher in second generation merozoites than in sporulated oocysts, unsporulated oocysts, or sporozoites, and the EteIF3s7 protein was barely detectable in unsporulated oocysts. Our immunofluorescence analysis showed that the EteIF3s7 protein was uniformly distributed throughout the cytoplasm of sporozoites. After sporozoites were incubated in complete medium, the EteIF3s7 protein localized to the anterior region of the parasite. Following the first schizogenous division, the protein was uniformly dispersed in trophozoites, immature schizonts, and mature schizonts, and the EteIF3s7 protein was observed to be closely associated with the parasitophorous vacuole membrane. An anti-rEteIF3s7 polyclonal antibody inhibited the ability of E. tenella to invade DF-1 cells, which suggested that EteIF3s7 might be involved in host cell invasion and required for the growth of the parasite in the host.

Molecular characterization and analysis of a novel protein disulfide isomerase-like protein of Eimeria tenella

Protein disulfide isomerase (PDI) and PDI-like proteins are members of the thioredoxin superfamily. They contain thioredoxin-like domains and catalyze the physiological oxidation, reduction and isomerization of protein disulfide bonds, which are involved in cell function and development in prokaryotes and eukaryotes. In this study, EtPDIL, a novel PDI-like gene of Eimeria tenella, was cloned using rapid amplification of cDNA ends (RACE) according to the expressed sequence tag (EST). The EtPDIL cDNA contained 1129 nucleotides encoding 216 amino acids. The deduced EtPDIL protein belonged to thioredoxin-like superfamily and had a single predicted thioredoxin domain with a non-classical thioredoxin-like motif (SXXC). BLAST analysis showed that the EtPDIL protein was 55–59% identical to PDI-like proteins of other apicomplexan parasites. The transcript and protein levels of EtPDIL at different development stages were investigated by real-time quantitative PCR and western blot. The messenger RNA and protein levels of EtPDIL were higher in sporulated oocysts than in unsporulated oocysts, sporozoites or merozoites. Protein expression was barely detectable in unsporulated oocysts. Western blots showed that rabbit antiserum against recombinant EtPDIL recognized only a native 24 kDa protein from parasites. Immunolocalization with EtPDIL antibody showed that EtPDIL had a disperse distribution in the cytoplasm of whole sporozoites and merozoites. After sporozoites were incubated in complete medium, EtPDIL protein concentrated at the anterior of the sporozoites and appeared on the surface of parasites. Specific staining was more intense and mainly located on the parasite surface after merozoites released from mature schizonts invaded DF-1 cells. After development of parasites in DF-1 cells, staining intensified in trophozoites, immature schizonts and mature schizonts. Antibody inhibition of EtPDIL function reduced the ability of E. tenella to invade DF-1 cells. These results suggested that EtPDIL might be involved in sporulation in external environments and in host cell adhesion, invasion and development of E. tenella.

Analysis of humoral immune response and cytokines in chickens vaccinated with Eimeria brunetti apical membrane antigen-1 (EbAMA1) DNA vaccine

This study aimed to determine the changes of cytokines, specific serum IgG and several parameters in chickens vaccinated with DNA vaccine encoding Eimeria brunetti apical membrane antigen-1 (EbAMA1) antigen. Two-week-old chickens were divided into five groups (four groups for experiment) randomly. Experimental groups of chickens were immunized with DNA vaccine while control group of chickens were injected with pVAX1 plasmid alone or TE buffer solution. All immunizations were boosted 2 weeks later. The EbAMA1 specific IgG antibody responses were measured at weeks 1-6 post-second immunizations and several parameters were also identified. The result showed that the antibody titers in chickens vaccinated with DNA vaccines were significantly different from those of the control groups 1 week after the second immunization and reached the maximum values 3 weeks post-second immunization. IFN-γ concentration was increased the highest level against EbAMA1 of all chickens vaccinated with vaccines up to 56-fold, follow by the specific IgG antibody levels were increased 10-17-fold compared with those of TE solution and plasmid (pVAX1) control chickens 1-6 weeks post-second immunization. In case of the levels of IL-10 and IL-17 was increased in experimental chickens with 4-5-fold. Even though it was statistically significant, TGF-β and IL-4 levels were higher in vaccinated than unvaccinated chickens. The results suggested that DNA vaccines encoding E. brunetti apical membrane antigen-1 (EbAMA1) could increase serum specific IgG antibody and cytokines concentration and could give protection against E. brunetti infection.

A selective review of advances in coccidiosis research

Coccidiosis is a widespread and economically significant disease of livestock caused by protozoan parasites of the genus Eimeria. This disease is worldwide in occurrence and costs the animal agricultural industry many millions of dollars to control. In recent years, the modern tools of molecular biology, biochemistry, cell biology and immunology have been used to expand greatly our knowledge of these parasites and the disease they cause. Such studies are essential if we are to develop new means for the control of coccidiosis. In this chapter, selective aspects of the biology of these organisms, with emphasis on recent research in poultry, are reviewed. Topics considered include taxonomy, systematics, genetics, genomics, transcriptomics, proteomics, transfection, oocyst biogenesis, host cell invasion, immunobiology, diagnostics and control.

Identification and characterization of an Eimeria-conserved protein in Eimeria tenella

The precocious lines of Eimeria spp. have unique phenotypes. However, the genetic basis of the precocious phenotype is still poorly understood. The identification of Eimeria genes controlling the precocious phenotype is of immense importance in the fight against coccidiosis. In the present study, a novel gene of Eimeria maxima was cloned using rapid amplification of cDNA ends (RACE) based on the expressed sequence tag (EST). Homologous genes were also found in Eimeria tenella and Eimeria acervulina. Alignment of the amino acid sequences from E. tenella, E. maxima, and E. acervulina showed 80-86 % identity, demonstrating a conserved protein in different Eimeria spp. This gene, designated Eimeria-conserved protein (ECP), contained 235 amino acids with a predicted molecular mass of 25.4 kDa and had 100 % identity with one annotated protein from E. maxima (Emax_0517). Real-time PCR and Western blot analysis revealed that the expression of ECP at mRNA and protein level in E. tenella is developmentally regulated. Messenger RNA levels from the ECP gene were higher in sporozoites than in other developmental stages (unsporulated oocysts, sporulated oocysts, and second-generation merozoites). Expression of ECP protein was detected in unsporulated oocysts, increased in abundance in sporulated oocysts, and was most prominent in sporozoites. Thereafter, the level of the ECP protein decreased, and no ECP-specific protein was detected in second-generation merozoites. Immunostaining with anti-rECP indicated that ECP is highly concentrated in both refractile bodies (RB) of free sporozoites, but is located at the apical end of the sporozoites after invasion of DF-1 cells. The specific staining of the ECP protein becomes more intense in trophozoites and immature first-generation schizonts, but decreases in mature first-generation schizonts. Inhibition of the function of ECP using specific antibodies reduced the ability of E. tenella sporozoites to invade host cells. Compared with the parent strain, both mRNA and protein expression levels in the sporulated oocyst were downregulated in the precocious line of E. tenella. These results suggest that ECP may be involved in invasion and development of the first-generation merogony stage of E. tenella. Findings of downregulation of ECP mRNA and protein expression in the precocious line enrich the study of the precocious phenotype of Eimeria.

An Eimeria vaccine candidate based on Eimeria tenella immune mapped protein 1 and the TLR-5 agonist Salmonella typhimurium FliC flagellin

Immune mapped protein-1 (IMP1) is a new protective protein in apicomplexan parasites, and exits in Eimeria tenella. But its structure and immunogenicity in E. tenella are still unknown. In this study, IMPI in E. tenella was predicted to be a membrane protein. To evaluate immunogenicity of IMPI in E. tenella, a chimeric subunit vaccine consisting of E. tenella IMP1 (EtIMP1) and a molecular adjuvant (a truncated flagellin, FliC) was constructed and over-expressed in Escherichia coli and its efficacy against E. tenella infection was evaluated. Three-week-old AA broiler chickens were vaccinated with the recombinant EtIMP1-truncated FliC without adjuvant or EtIMP1 with Freund's Complete Adjuvant. Immunization of chickens with the recombinant EtIMP1-truncated FliC fusion protein resulted in stronger cellular immune responses than immunization with only recombinant EtIMP1 with adjuvant. The clinical effect of the EtIMP1-truncated FliC without adjuvant was also greater than that of the EtIMP1 with adjuvant, which was evidenced by the differences between the two groups in body weight gain, oocyst output and caecal lesions of E. tenella-challenged chickens. The results suggested that the EtIMP1-flagellin fusion protein can be used as an effective immunogen in the development of subunit vaccines against Eimeria infection. This is the first demonstration of antigen-specific protective immunity against avian coccidiosis using a recombinant flagellin as an apicomplexan parasite vaccine adjuvant in chickens.

Eimeria maxima: efficacy of recombinant Mycobacterium bovis BCG expressing apical membrane antigen1 against homologous infection

Coccidiosis is one of the most important protozoan diseases and inflicts severe economic losses on the poultry industry. The aim of this study was to evaluate the capacity of Bacillus Calmette-Guerin (BCG) to deliver apical membrane antigen1 (AMA1) of Eimeria maxima to stimulate specific cellular and humoral immune responses in chickens. Day-old birds were immunized twice with rBCG/pMV261-AMA1, rBCG/pMV361-AMA1, or BCG via oral, intranasal, and subcutaneous routes and then orally challenged with homologous E. maxima sporulated oocysts. Gain of body weight, fecal oocyst output, lesion scores, serum antibody responses, numbers of splenocyte CD4(+) and CD8(+) T cells, and gut cytokine transcript levels were assessed as measures of protective immunity. Challenge experiments demonstrated that rBCG vaccination via intranasal or subcutaneous routes could increase weight gain, decrease intestinal lesions, and reduce fecal oocyst shedding, and the subcutaneous and intranasal routes were superior to the oral route based on the immune effects. Furthermore, intranasal rBCG immunization could also lead to a significant increase in serum antibody, the percentage of CD4+ and CD8+ T lymphocyte cells, and the levels of IL-1β, IFN-γ, IL-15, and IL-10 mRNAs compared with the control group. These results suggested that intranasal rBCG immunization could induce a strong humoral and cellular response directed against homologous E. maxima infection. This study provides data for the use of rBCG to develop a prophylactic vaccine against coccidiosis.

High-throughput RNA sequencing profiles and transcriptional evidence of aerobic respiratory enzymes in sporulating oocysts and sporozoites of Eimeria tenella

Seven species of Eimeria are responsible for coccidiosis in chickens. Eimeria tenella is one of the most pathogenic parasites since it is associated with high mortality and great economic impact. The life cycle of the parasite includes development in the environment and in the intestinal tract. We conducted RNA sequencing using a next generation sequencer to obtain transcriptome information from the sporulating oocysts, and sporozoites. We collected 2.8 million 75 bp reads of a short-tag sequence, and 25,880 contigs were generated by the Oases assembler. A Blastx search of GenBank databases revealed that 7780 contigs (30.1%) had significant homology with deposited sequence data (E-value <1e-6); among these contigs, 6051 contigs were similar to those of Toxoplasma gondii while only 513 contigs (6.6%) were similar to those of E. tenella. After an orthological analysis conducted with the UniProt database of T. gondii, 6661 contigs were distributed within the categories of cellular components (1528 gene categories), biological processes (861 gene categories), and molecular functions (241 gene categories). The significantly matched contigs contained high numbers of enzymes associated with glycolysis, TCA, and the pentose-phosphate pathway. Most of the enzymes, measured by quantitative reverse transcription-PCR, were up-regulated in sporulating stage. These results suggest that the intracellular carbohydrate amylopectin could be used as an energy source for ATP production including glycolysis and the pentose-phosphate pathway, which generates NADPH and pentoses. Our data also suggest that Eimeria might possess a partial or similar pathway to the TCA cycle essential for aerobic respiration. Furthermore, the newly annotated and non-annotated contigs might contain E. tenella-specific or novel sequences.